Use of "Afghani" as an adjective

So we know that the noun "Afghan" is preferred over "Afghani" when it comes to describing the people of Afghanistan, but what's the scoop for using it as an adjective? For example, is saying an "Afghani carpet" incorrect, offensive, both or neither, as opposed to an "Afghan carpet"?

Context: A rather lively debate on Travel.SE about whether using the term "Afghani passport" in a newspaper article is a mark of cluelessness.

The term Afghan is both the noun (for people and things) and the adjective in Dari (the variety of Persian used in Afghanistan. The term afghani is a separate noun, referring to a small unit of currency.

We have evidence in English from usage much earlier than the events of post-1978 showing Afghan as both a noun and an adjective, e.g. Afghan carpet, Afghan hound, and a knitted or crocheted Afghan (lap blanket), thanks to contacts between the Raj (British colonists of the Subcontinent) and Afghans.

I am frustrated when I hear academics using afghani as a noun (other than to mention the coin) and adjective with their students, thus perpetrating the error.

I had cultural sensitivity training for work in Afghanistan. I was taught that Afghan is the word you are looking for. It describes a person or thing from Afghanistan. Afghani is the money.

The Afghan rug cost me 500 Afghani.

The CIA world factbook gives Afghan. There's a Slate article here that gives more on the topic. Afghan is definitely the correct word.